1. Field of the Invention
The present invention is generally related to a system for monitoring a galvanic protection system and, more particularly, to a monitor system which provides an easily recognizable signal representing the current state of a galvanic protection system without the need for operator.
2. Description of the Prior Art
It is widely known to those skilled in the art that certain submerged components can experience galvanic corrosion when used in conjunction with a marine vessel, such as a boat. Various types of corrosion prevention systems are available to prevent galvanic corrosion of marine propulsion system components. These include sacrificial anodes and electrical systems that inhibit galvanic corrosion of marine components. When connected properly and operated in conformance with suggested procedures, these known prevention systems work adequately. However, if the galvanic corrosion system is not working properly, a boat operator generally will not be aware of this condition without some active involvement by the boat operator. As an example, a sacrificial anode may be missing or so severely depleted that it is ineffective. In addition, an electrical prevention system can experience a broken wire or a connection that is inadvertently loosened. Although one system is available in the prior art that permits an operator to actively cause a circuit to be completed to check certain characteristics of one particular type of electrical corrosion prevention system, no passive monitor is currently available that automatically informs a boat operator of a problem in a galvanic protection system without requiring the operator to first request the monitor to check the system.
U.S. Pat. No. 4,117,345, which issued to Balcom on Sep. 26, 1978, describes a marine ground isolator. The isolator selectively completes the current path through a ground connection. The preferred of the isolator includes a switch circuit connected in series between two portions of the ground connection and arranged so as to complete the current path therethrough only in response to an applied control signal. It further comprises means for monitoring the potential between the two portions of the ground connection and for applying the control signal to the switch circuit only when the absolute magnitude of the dc potential exceeds a first value or when the ac potential exceeds a second value.
U.S. Pat. No. 5,627,414 which issued to Brown et al on May 6, 1997, describes an automatic cathodic protection system using galvanic anodes. The automatic system uses sacrificial galvanic anodes to provide a controlled and optimum amount of cathodic protection against galvanic corrosion on submerged metal parts. Intermittently pulsed control circuitry enables an electro-mechanical servo system to control a resistive element interposed between the sacrificial anodes and the electrically bonded underwater parts. In an active mode of operation, a current is applied directly to the anodes to quickly establish the proper level of correction which is maintained during the passive mode. Incremental corrections are made over a period of time to provide stabilization of the protection and to conserve power. A visual indication of the amount of protection is available at all times. Circuitry and indicating devices are included which facilitate location and correction of potentially harmful stray currents and to prevent loss of sacrificial anodes to nearby marine structures.
U.S. Pat. No. 5,840,164, which issued to Staerzl on Nov. 24, 1998, discloses a galvanic isolator used to protect against galvanic corrosion of a submersible metal marine drive. The galvanic isolator is positioned between shore ground and boat ground to prevent the flow of destructive galvanic currents between the shore ground and the boat ground, while maintaining the safety function of neutral ground. The galvanic isolator of the invention includes a blocking element positioned between the boat ground and the shore ground that can be switched between an open and a closed state by a trigger circuit. The trigger circuit closes the blocking element when the difference between the boat ground and the shore ground exceeds a threshold value, such as 1.4 volts. During operation of the galvanic isolator during the high fault current condition, power is dissipated only by the blocking element, rather than by the combination of the blocking element and the trigger device. In this manner, the galvanic isolator reduces the amount of power dissipated during high current conditions and therefore reduces the amount of heat generated by the galvanic isolator.
U.S. Pat. No. 5,747,892, which issued to Staerzl on May 5, 1998, discloses a galvanic isolator fault monitor. The system and method for testing and monitoring the operation of a galvanic isolator are provided by this device. The isolator is positioned between shore ground and boat ground to prevent the flow of destructive galvanic currents between the shore ground and the boat ground. The monitoring system transmits a test current through the galvanic isolator at specific time intervals to test the effectiveness of the galvanic isolator. The monitoring system includes a first counter that outputs an enabling signal after a period of time. The enabling signal allows a test current to flow through the galvanic isolator for a brief period of time determined by a second counter. As the test current flows through the galvanic isolator, a current sensing circuit measures the test current and activates an alarm if the test current flowing through the galvanic isolator falls outside a predetermined range. In this manner, the monitoring system of the invention monitors and periodically tests a galvanic isolator.
U.S. Pat. No. 4,528,460, which issued to Staerzl on Jul. 9, 1985, describes a cathodic protection controller. The control system for cathodically protecting an outboard drive unit from corrosion includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water.
U.S. Pat. No. 3,953,742, which issued to Anderson et al on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for marine propulsion device. The monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode lamp or other light source between the controller output and ground so that the controller current may, when tested, be used to operate the light source in order to confirm that power is available to the anode.
The United States patents described above are hereby explicitly incorporated by reference in the description of the present invention.
A booklet titled "Everything you need to know about marine corrosion" and published by the Quicksilver Marine Parts and Accessories Division of Mercury Marine, which is a division of the Brunswick Corporation, provides a detailed description on the electrochemistry of marine corrosion and also describes numerous techniques and devices available for the prevention of marine corrosion.
Notwithstanding the existence of many different systems for the prevention of galvanic corrosion of marine components, it would be significantly beneficial if a monitoring system could be provided that did not require active participation by a boat operator but provided a visual signal of the present operating condition of the galvanic corrosion prevention system.